OpenAI Launches GPT-5.4-Cyber — Restricted Cybersecurity Model to Counter Anthropic's Mythos
The AI cybersecurity arms race just got a lot more official. On April 14, 2026, OpenAI announced GPT-5.4-Cyber — a fine-tuned variant of GPT-5.4 built specifically for defensive cybersecurity work, available exclusively to vetted defenders through a new restricted-access program called Trusted Access for Cyber (TAC). This isn’t a subtle product update. It’s a direct and deliberate response to Anthropic’s Claude Mythos Preview release the week prior — a model Anthropic kept out of general availability specifically because of its potential for abuse by threat actors. OpenAI’s counter-move: stake out the “guardrails-first” lane and argue that today’s safeguards are already sufficient, while simultaneously releasing a cyber-permissive model for the defenders who need it most. ...